Process for melting down amalgams of aluminum or its alloys and for removing the mercury therefrom



'June 11, 1957 -G ES NER 2,79 ,498

M s 5 PROCESS FOR MELTING DOWN AMALGAMS OF ALUMINUM OR ITS ALLOYS AND FOR REMOVING THE MERCURY THEREFROM Filed Jan. 24, 1956 2 Sheets-sheaf. 1

Dr: Georg M ssner IN V EN TOR.

BY j/"lM/W/ -A TTORIVEY G. MESSNER June 11, 1957 PROCESS FOR MELTING DOWN AMALGAMS OF ALUMINUM OR ITS ALLOYS AND FOR REMOVING THE MERCURY THEREFROM 1956 2 Sheets-SheetZ Filed Jan. 24

0/: Georg Messner IN VENT 0R.

United States Patent PROCESS FOR MELTING DOWN AMALGAMS OF ALUMINUM OR ITS ALLOYS AND FOR REMOV- IN G THE MERCURY THEREFROM Georg Messner, Sao Paulo, Brazil Application January 24, 1956, Serial No. 561,086

Claims priority, application Switzerland October 31, 1%9

7 Claims. (Cl. 75-68) The present invention relates to a new method for melting down aluminum amalgams or amalgams of aluminum alloys and of freeing them from the mercury contained therein. This application is a continuation in part of my co-pending application Ser. No. 191,094, filed October 19, 1950, now abandoned.

The processes hitherto in use for removing mercury from amalgams of aluminum or its alloys are not satisfactory. According to one known process the melting down of aluminum amalgam is carried out in charges, by filling a closed melting crucible with aluminum amalgam, raising the temperature above the melting point of aluminum, and then pouring the material. This process is slow and the amount of aluminum recovered in a certain time is either quite small or, if larger outputs are desired, the apparatus has to be very large. Moreover, injury may occur to the health of the workers from mercury vapor when handling the materials.

The melting time could be shortened by continuously feeding the aluminum amalgam into a permanently maintained pool of fluid aluminum or aluminum alloy; However, on feeding the amalgam into the liquid metal pool, the major portion of the mercury explosively turns into vapor which leads to difficulties both as a result of the sudden rise in pressure and of the spattering of the aluminum.

In general, processes hitherto in use melt down the amalgam containing mercury and attempt to evaporate mercury from the liquid. Such evaporation depends upon the tendency of the mercury to either remain with the aluminum alloying component or to escape from the amalgam as a function of temperature and time. As the proportion of mercury drops to a lower value, it appears to have a persistent aflinity for the aluminum and it must be superheated or overheated by a considerable degree. This causes splashing due to the violent liberation of the mercury vapors from the pasty liquid.

For the purposes of the recovery of aluminum from such amalgam, it is technically required that traces of mercury be completely eliminated from the product recovered. Operations, therefore, in the prior art which employ distillation columns and the like for the handling of the mercury alloy in liquid or paste form need to be carried out very slowly in order to prevent splattering, reduce mechanical losses of the aluminum product which it is desired to recover, and to minimize, as much as possible, the danger to the workers because of the high toxicity of mercury vapor.

It has now been found that the above mentioned difliculties can be eliminated by providing a process for melting down the amalgams of aluminum or its alloys, while practically completely removing the mercury from the same, by feeding the amalgams in a preheated state in lump form through a melting device having zones of different temperature and placing in the path of the amalgams means for temporarily obstructing their forward movement for a sufficient period of time to cause 2,795,498 Patented June 11, 1957 the main amount of the mercury to evaporate before the amalgam melts down.

It is surprising that the controlled evaporation of mercury from amalgams in lump form should not only reduce the health hazard to workers, but that it should also completely prevent the explosive evaporation of mercury from liquid or pasty residues.

In carrying out the invention, a stream of some inert non-oxidizing gas e. g. argon or hydrogen, may be passed in counterflow to the material to be melted. The gas is used for rinsing the mercury vapor formed out of the melting apparatus and thereby accelerates the removal of the mercury from the aluminum or aluminum alloy. The rinsing gas may be circulated through the apparatus.

As a means for temporarily obstructing the movement of the amalgam feed, a perforated plate is preferably used, having openings which are sufficiently small in relationship to the lump-size of the amalgam to prevent the lumps from passing through before the main part of the mercury has evaporated.

The size of the amalgam lumps or grains may vary from about 2 mm. to about 10 mm., but it should be understood that these figures are not given by way of limitation.

The apparatus for carrying out the process according to the invention is illustrated in the accompanying drawings in several embodiments, but it should be understood that I do not limit my invention to the exact method or devices described herein, and that many modifications may be made without departing from the spirit of my invention and the scope of the claims as appended.

In the drawings:

Fig. 1 is an embodiment of the apparatus with vertically arranged furnace or shaft converter;

Fig. 2 is another embodiment with a horizontally arranged tube, and

Fig. 3 is yet another embodiment with an inclined tube.

In the different figures, similar elements are designated by the same reference numerals.

The apparatus according to the invention, as illustrated in Fig. 1, is provided with an upright outer shell 14 and a concentric converter casing 16, lined with coal. Mounted in the latter is a hopper 11 for feeding the material to be melted into the furnace. A look 12 prevents access of air.

Near the feed end of the furnace tube, an outlet pipe 13 is arranged through which the hydrogen and the mercuryvapor evolved in the process can escape. At the upper end of the shell an exhaust pipe 15 carries off the heating gases.

Arranged within the furnace casing 16 are a perforated plate 17 and a plurality of trays 18 which form obstacles for the flow of the aluminum alloy fed through hopper 11. At the lower end of the furnace, a pipe 19 serves as inlet for hydrogen or argon, While a flue 20 is provided for admitting heating gases, from a source not shown in the drawing, to the heating space 23. The drain for carrying off the purified aluminum or the pure alloy metals is designated by 21, a receptacle for collecting the same by 22.

The horizontally arranged crucible or furnace shown in Fig. 2 is similar in most elements except for the absence of trays, which are not needed in this embodiment. Any known means of heating can be applied, either heating by combustion gases, in a way shown in Fig. 1, or electric heating, or other known devices.

In the embodiment of the furnace shown in Fig. 3, a feeding means is shown for material which is in the form of plastic lumps. In this case, the hopper 11 connects with a short pressure nozzle 25. In the interior of the slightly inclined tube 16, which is lined with a material rich in alumina, a worm 24 is arranged serving as an obstacle to the flow of aluminum amalgam, as more fully described below in Example 3. j

The feeding of the material to be melted into the furnace must take place under the exclusion of air or gas, either by means of a lock, or, if the amalgam to be fed is sufiiciently plastic, by pressing it through an extrusion nozzle.

The operation of the device is described in the following examples, in which Examples 1 and 2 can be carried out in the furnace embodiments illustrated in Figs. 1 and 2.

Example I Aluminum amalgam containing 70% aluminum and 30% mercury is dropped in form of grains or lumps from above into the shaft converter 16 through hopper 11 and lock 12. The grains have a size of approximately 5 mm. The amalgam charged to the furnace has a temperature of 250300 C. The temperature of the material rises as it approaches plate 17, and at a certain distance of the same the boiling temperature of mercury, 360 C., is reached. in this zone, the major portion of the mercury, or at least 90%, distillsotf. In the meanwhile, the amalgam, which becomes increasingly poorer in mercury, has reached plate 17.. As soon as the melting point of aluminum (app. 658 C.) is reached, the latter is capable of flowing through the perforations of the plate in liquid form and reaches the first tray 18 containing molten aluminum with low mercury content, without there being a danger of a sudden impact on the molten mass with consequent splashing. At the lower end of the shaft converter, a hydrogen or argon streamvmay be introduced through pipe 19, which carries upward the mercury vapor generated in the furnace and conveys the same to a watercooled mercury vapor condenser.

The shaft converter is heated from the outside by gas in such a manner that the liquid aluminum flowing from the furnace is heated to a temperature of between 700 and 750 C. At the perforated plate 17 the melting temperature of aluminum is then automatically reached without the need of any special adjustment of the heating. Beneath the perforated plate, the trays 18, made of coal, increase the length of stay of the aluminum in the furnace, thereby subjecting the liquid metal to an intensified contact with the rinse-gas. The liquid metal flowing from the lower end of the furnace has a residual content of mercury of less than by weight.

While the temperature of the arriving amalgam has been given as 250300 C., it may also be somewhat higher or lower without changing the operation. However, if the amalgam had a lower temperature as it is fed to the hopper, a larger amount of heat would have to be transferred to the upper end of the furnace.

The principal object of the present invention would still be attained, i. e. the plate 17 would delay the downward movement of the amalgam until most of the mercury, or from 90-95%, has evaporated and the melting temperature of the mixture, aluminum plus a small amount of mercury, has been reached, which melting temperature almost equals that of pure aluminum. As the melt descends, the remaining mercury will gradually escape, the main amount of mercury having already been removed by evaporation at and above the perforated plate 17.

The velocity of evaporation of the liquid mercury compound approaches the velocity Which may be computed according to the laws of kinetics, as far as the surface zones of the amalgam lumps are concerned. As the temperature of a lump of amalgam approaches the boiling point of mercury at atmospheric pressure, the velocity of evaporation comes close to that of boiling. Within the lumps of amalgam and in the interior portions of the amalgam pile, mercury vapor will escape at a lower rate. Consequently, the control of the particle size of the amal gam permits the removal of mercury from the interior substantially as fast as at the exterior.

Example 2 An amalgam of an aluminum alloy containing:

40% mercury 42% aluminum 12% copper 1.5% magnesium 1.8% manganese 1.8% iron 0.9% silicon obtained in the extraction of aluminum with mercury from aluminum scrap and subsequent centrifugal removal of the major portion of mercury, is introduced in the form of crumbs of about 3 mm. into a shaft furnace as illustrated in Figs. 1 or 2, and as described in Example 1.

The aluminum-copper alloy containing less than.l0% of mercury reaches its melting temperature at the perforated plate 17. It is lower than the melting point of pure aluminum. The fluid metal flowing from the furnace has a mercury content of less than Iii- Example 3 Crumbs of aluminum amalgam containing 35% of aluminum and of mercury obtained by aluminum extraction and subsequent centrifugal treatment of the resulting amalgam paste, are processed in a revolving tube furnace, illustrated in Fig. 3. The amalgam crumbs are fed, with exclusion of air, through nozzle 25 to the receiving end of the closed tube 16 with its lining rich in alumina. The non-metallic worm 24, arranged in the upper third of the tube, consists of about 1 /2 turns so designed as if it were to return the contents to the inlet. The heating of the tube is adjusted in such a manner that the amalgam remains solid above the worm for a a period long enough to allow the main part of the mercury to evaporate. Thereafter, aluminum melts down and collects at the lower end of the tube 16, from where it is syphoned off into the receptacle 22 in an air-tight manner. The wash-gas entering at 19 accelerates the removal of the mercury vapor. The heating is regulated in such a manner that the liquid aluminum at the delivery end of the oven has a temperature of 700-750 C. Its mercury content lies below 10 While in the above example the method of the inven tion has been described with reference to furnace embodiments illustrated in the drawings, it should be understood that the novel process of controlled evaporation of mercury can be carried out in other apparatuses as well, provided the main amount of mercury present in the amalgam is removed by evaporation before the melting of the amalgam lumps occurs.

A further very important feature of the invention is the fact that the operation is carried out at atmospheric pressure. This is an important improvement since many of the processes used up to now are carried out under reduced pressure which requires expensive equipment and great care in the operation.

The mercury vapors escaping from the melting device may be withdrawn to a condensing system, if desired by means of a vacuum line.

What I claim is:

1. A process for melting down amalgams of aluminum and its alloys with simultaneous removal of mercury by distillation, which comprises feeding heated amalgamated lumps to a melting device and through a plurality of different temperature zones therein, temporarily obstructing the forward movement of said material to be melted in a first zone for a suflicient period of time to evaporate the main amount of mercury while maintaining the amalgam feed in lump form, thereafter heating said feed material now containing only residual amounts of mercury, to its melting point, allowing the molten material to move through said heating device at a temperature 5 gradually increasing to 700-750 C., and collecting the metals thus obtained practically free from mercury at the bottom of the device.

2. A process for removing mercury from aluminum amalgams to recover aluminum and its alloys in a condition free from mercury, comprising feeding said amalgam in lump form to a first zone at a temperature between about 250 C. and 360 C. for a suflicient period of time to evaporate at least 90% of the mercury, said lumps diminishing in size during the evaporation of mercury therefrom in said first zone, until they reach a smaller size, interposin-g in the path of said lumps a perforated plate, having holes smaller than said lumps which retains said lumps in said first zone until substantially all of said mercury is removed and thereafter heating said lumps 15 to their melting point to permit them to pass through the perforations in said plate whereby there is recovered aluminum and its alloys in a form substantially free from mercury.

the temperature in said first zone from 250-360 C 4. The process according to claim 3, wherein the size of the amalgam grains is from 2 mm. to 10 mm. in diameter.

5. The process set forth in claim 1 which comprises introducing an inert washing gas in counterflow to the material to be melted during its travel through the melting device.

6. The process set forth in claim 1 wherein the operation is carried out at atmospheric pressure.

7. The process set forth in claim 1 wherein the material to be melted is introduced with exclusion of air.

References Cited in the file of this patent UNITED STATES PATENTS Dujchak et a1 Nov. 17, 1931 Menardi Jan. 9, 1940 OTHER REFERENCES Metal Industry, Sept. 20, 1946, pages 236, 239. 

1. A PROCESS FOR MELTING DOWN AMALGAMS OF ALUMINIU AND ITS ALLOYS WITH SIMULTANEOUS REMOVEL OF MERCURY BY DISTILLATION, WHICH COMPRISES FEEDING HEATED AMALGAMATED LUMPS TO A MELTING DEVICE AND THROUGH A PLURALITY OF DIFFERENT TEMPERATURE ZONES THEREIN, TEMPORARILY OBSTRUCTING THE FORWARD MOVEMENT OF SAID MATERIAL TO BE MELTED IN A FIRST ZONE FOR A SUFFICIENT PERIOD OF TIME TO EVAPORATE THE MAIN AMOUNT OF MERCURY WHILE MAINTAINING THE AMALGAM FEED IN LUMP FORM, THEREAFTER HEATING SAID FEED MATERIAL NOW CONTAINING ONLY RESIDUAL AMOUNTS OF MERCURY, TO ITS MELTING POINT, ALLOWING THE MOLTEN MATERIAL TO MOVE THROUGH SAID HEATING DEVICE AT A TEMPERATURE GRADUALLY INCREASING TO 700-750* C., AND COLLECTING THE METALS THUS OBTAINED PRACTICALLY FREE FROM MERCURY AT THE BOTTOM OF THE DEVICE. 